Performance of the SRK/T formula using A-Scan ultrasound biometry after phacoemulsification in eyes with short and long axial lengths

Effect of Intraocular Lens Power Calculation Formula Optimization in the Sum-of-Segments Optical Biometer

Purpose

We evaluated the effect of optimization of the intraocular lens (IOL) power calculation formula SRK/T and Barrett Universal II (BU II) in long eyes (≥26 mm: group L) and short eyes (≤22 mm: group S) using axial length calculated from segmented refractive indices (SRI).

Setting

Multicenter study at five sites in Japan.

Design

Retrospective observational study.

Methods

This study included 461 eyes of 461 patients (mean age 73.8 ± 8.4 years) who underwent cataract surgery. The predicted refractive error (PRE) was compared between the SRI (ARGOS) and the equivalent refractive index (ERI) biometers (IOLMasterTM700). The patients were randomly divided into two groups, a learning group and a validation group. The optimization constants were determined in the learning group, and the optimization constants were subsequently applied to the validation group and compared with the ERI biometer results.

Results

Using both SRK/T and BU II, the validation group's PRE using optimization constants for the SRI biometer in group L was significantly smaller than that using the ERI biometer (p<0.001, p<0.01). In group L, the arithmetic PRE of Barrett UII formula with SRI showed a significant improvement after optimization compared to before optimization (p<0.0001). In group S, the arithmetic PRE of SRK/T and Barrett UII formula with SRI showed a significant improvement (p<0.0001, p<0.0001).

Conclusion

In long and short eyes, the current study revealed that optimization of the SRK/T and Barrett formula constants for the SRI biometer was beneficial to achieve accurate refractive outcomes after cataract surgery.

Comparison of Refractive Prediction Error by Axial Length in Flanged Intrascleral Intraocular Lens Fixation

Purpose

To evaluate the refractive prediction error in flanged intrascleral intraocular lens (IOL) fixation using the SRK/T formula and compare the axial length using a single IOL.

Methods

Seventy-six eyes from 70 patients (45 males and 25 females) were included in this study. The mean age at the time of surgery was 73.4 ±12.3 years. The patients underwent flanged IOL fixation using a PN6A (Kowa). All surgeries were performed by two surgeons (Y. K. and T. O.) between Jan 2020 and Dec 2022 at Jikei University Daisan Hospital. IOL power was calculated using the SRK/T formula with IOL Master 700 (Carl Zeiss) as the bag power. The recommended value of 119.0 was used for the A-constant. The actual refractive spherical equivalent was calculated and compared with preoperative predictions. Refractive prediction errors were defined as the deviation of the actual postoperative spherical equivalent refraction in diopters from the predicted preoperative spherical equivalent refraction. The patients were divided into three groups according to axial length: <22.0 mm (short eyes), 22.0-24.5 mm (medium eyes), and >24.5 mm (long eyes), and the refractive prediction errors and mean absolute errors were compared.

Results

The mean refractive prediction error was -0.20 ± 0.52D. The mean absolute error was 0.44 ± 0.33D. The mean refractive prediction errors were not significantly different between the 22.0-24.5 mm (medium eyes) and >24.5 mm (long eyes) groups. (P=0.06) The mean absolute errors were not significantly different between the two groups (P=0.10).

Conclusion

The SRK/T formula worked well regardless of whether the eyes were medium or long according to the axial length in the flanged intrascleral IOL fixation.

Intraocular lens power calculation in eyes with a shallow anterior chamber depth and normal axial length

We compared the accuracy of three intraocular lens (IOL) calculation formulas in eyes with a shallow anterior chamber depth (ACD) and normal axial length (AXL) and control eyes. We retrospectively reviewed eyes with a shallow ACD (<2.5 mm from the corneal epithelium) with normal AXL (22.5≤AXL<24.0 mm) and controls (3.0≤ACD<3.5 mm and normal AXL). Prediction error (PE) and median absolute error (MedAE) were evaluated with SRK/T, Barrett Universal II (BUII), and Kane formulas after adjusting the mean PE to zero for all patients. Percentages of eyes achieving a PE within 0.25 to 1.00 D, and correlations between ACD, lens thickness (LT), and PE were analyzed. Thirty-five shallow ACD and 63 control eyes were included. PE in the shallow ACD group showed more hyperopic results with BUII and Kane but not with SRK/T compared to controls. Within the shallow ACD group, PE showed more hyperopic results in BUII and Kane compared to SRK/T. However, the standard deviation (SD) of PE among formulas was not different. In the shallow ACD group, SRK/T showed a higher percentage of PE within 0.25 D than BUII and Kane, but the percentages within 0.50 to 1.00 D were similar. PE was negatively correlated with ACD in BUII and Kane, and positively correlated with LT in all formulas. BUII and Kane may induce slight hyperopic shift in eyes with a shallow ACD and normal AXL. However, the performance of the three formulas was comparable in the shallow ACD group in terms of MedAE, the SD of PE, and the percentage of eyes achieving PE within 0.50 D.

Effectiveness, Sensitivity, and Specificity of Intraocular Lens Power Calculation Formulas for Short Eyes

Objectives:

Materials and Methods:

Results:

Conclusion:

THE EXACTNESS OF INTRAOCULAR LENS POWER CALCULATION FORMULAS FOR SHORT EYES AND CORRELATION BETWEEN METHOD ACCURACY AND EYEBALL AXIAL LENGTH

PURPOSE

To compare the accuracy of intraocular lens power calculation formulas and to examine the correlation of this exactness with the axial length for eyes shorter than 22.00 mm Methods: The data of hyperopic patients who underwent uneventful phacoemulsification between October 2015 and June 2019 were reviewed. The intraocular lens power for each patient was calculated using 6 formulas (Holladay1, SRK/T, Hoffer Q, Holladay 2, Haigis and Barrett Universal II) before cataract surgery. Postoperative refraction was measured, and refractive prediction error was calculated 3 months after phacoemulsification. The correlation between axial length and absolute error was evaluated.

RESULTS

Fifty-six patients (62 eyes) whose ocular axial length ranged between 20.58 mm and 21.97 mm were included in the study. The Hoffer Q formula achieved the lowest mean absolute error of 0.09 (±0.08 D). A significant correlation for the Hoffer Q (&#961; = -0.329, p = 0.009) and the SRK/T (&#961; = 0.321, p = 0.011) formula was observed.

CONCLUSIONS

1. The Hoffer Q formula obtained the lowest absolute error and was recommended for intraocular lens power calculation for eyeballs with axial length shorter than 22.0 mm. 2. The correlation between axial length and absolute error is a factor which should be considered when calculating intraocular lens power.

Refractive prediction by various intraocular lens formulas using optical biometry and effect of ocular parameters on their accuracy

Purpose:

To assess the prediction accuracy of intraocular lens (IOL) formulas and study the effect of axial length (AL), central corneal thickness (CCT), anterior chamber depth (ACD), and lens thickness (LT) on the accuracy of formulas using optic biometry.

Methods:

This study was performed on 164 eyes of 164 patients who underwent uneventful cataract surgery. Ocular biometry values were measured using Lenstar-900, and intraocular lens (IOL) power was calculated using the SRK/T, SRK II, Hoffer Q, Holladay 2, and Barrett Universal II formulas. We evaluated the extent of bias within each formula for different ocular biometric measurements and explored the relationship between the prediction error and the ocular parameters by using various IOL formulas.

Results:

The summarization of refractive prediction error and absolute prediction error for each IOL formulation was performed after adjusting the mean refractive error to zero. The deviation in the error values was minimum for SRK/T (0.265) followed by Holladay 2 (0.327) and Barret (0.382). Further, SRK/T had the lowest median (0.15) and mean (0.198) absolute error as compared to other formulations. For the above formulations, 100% of the eyes were in the diopter range of ±1.0. It was observed that the overall distribution of error was closer to zero for SRK/T, followed by Holladay 2 and then Barrett.

Conclusion:

In summary, we found that accuracy was better in SRK/T formula. We achieved a better understanding of how each variable in the formulas is relatively weighed and the influencing factors in the refraction prediction.

A-scan ultrasound in ophthalmology: A simulation tool

In the present study, we developed a computational tool for simulating the ophthalmological applications of A-scan ultrasound, including cataract characterisation and biometry. A-scan biometry is used to measure the axial length (AL) of the eye before cataract surgery to calculate the refractive power of the intraocular lens to be implanted. Errors in the measurement of the AL lead to post-surgical refractive errors. The simulation tool was developed using the k-Wave Matlab toolbox, together with a user-friendly interface developed in Matlab. Diverse error sources were evaluated. Constant ultrasound speed assumptions may introduce refractive errors of up to 0.6 D; by contrast, probe positioning errors had a lower impact, of up to 0.11 D. The correct identification of the Bruch's membrane is limited not only by axial resolution constraints but also by the low reflection coefficient at the retina/choroid interface. Regarding cataract characterisation, the amplitudes of the echoes reflected at the lens interfaces are sensitive to diverse cataract types and severities, and a more realistic representation could be obtained by using a higher resolution in the eye grid; however, the required computational times would make simulations impracticable when using personal computers. The simulation tool shows good versatility for evaluating diverse aspects of A-scan biometry.

Comparison between SRK/T and Haigis Formulas on Visual Acuity of Patient with Senile Cataract Post-Phacoemulsification

BACKGROUND: Cataract contributes to the most common cause of blindness worldwide. Cataract surgery is the most performed surgery in the world. To achieve optimal results, pre-operative biometric must be accurate and the use of a formula for measuring the strength of the intraocular lens (IOL) accurately must be used. SRK-T and Haigis are formulas applied in the calculation of IOLs. AIM: The objective of the study was to determine the evaluation of visual acuity after phacoemulsification using the SRK/T and Haigis formulas. METHODS: This was an observational prospective analytic study at Medan Baru Eye Hospital from June 2019 to August 2019. Following the examination, patients were required further follow-up on 7–30 days post-phacoemulsification. RESULTS: The number of subjects was 122 patients (122 eyes), 84 patients were observed, and 38 patients did not come back for control. This study was within the value of p = 0.053. Prediction of refractive errors after phacoemulsification for myopia identified using SRK/T formula was more common, resulting in 3 eyes (75.0%) compared to the Haigis formula. On contrary, the prediction for emetropia was mostly discovered on Haigis formula which amounted to 41 eyes (51.25%) compared to the SRK/T formula. CONCLUSIONS: There was no significant difference in predicting post-phacoemulsification visual acuity between SRK/T and Haigis formula.